What had you eaten, T42? It's very easy to get behind your carbohydrate needs with or without aspartame.
On the 300, can't remember.
On the 600 a banana sandwich for breakfast, a bit later a hot sausage roll, various bars, salami. Knock was quite a bit later, though: I thought I was OK with the drink.
I find ginger very easy to eat even through nausea, and the sugar is very fast. Doesn't last long, of course, but it gets your appetite started again.
One thing I've noticed is the necessity of something sweet after a meal. Eat a pizza or something meaty and digestion takes a toll on your calorie throughput: a fast-carb dessert bridges the slump and keeps you going. I've noticed this on setting out from home as well: I have a breakfast of ham & pasta, and at around 10 km I need a marzipan bar or similar otherwise I start to flag.